This invention relates to improved methods and apparatus to monitor patients who are being weaned from ventilator support, or who are being treated with non-invasive ventilatory support in order to obviate the need for invasive intubation and controlled ventilation.
Hillsman incorporates by reference his U.S. Pat. No. 3,991,304 "Respiratory Biofeedback and Performance Evaluation System" and U.S. Pat. No. 4,984,158 "Metered Dose Inhaler Biofeedback Training and Evaluation System" and U.S. Pat. No. 5,582,182 "Abnormal Dyspnea Perception Detection System and Method." It has been discovered that full scale calibration of the breathing volume on the display ordinate axis and full scale display of the breathing rate on the abscissa axis is a particularly powerful standardized means to present breathing patterns for patient learning (See: "A Visual Biofeedback Method to Define and Teach Breathing Patterns;" Hillsman, Deane; Biological Psychology, v.43, Issue 3, Jun. 28, 1996, p.261) and "Clinical Experience With a Visual Biofeedback Method in COPD Rehabilitation;" Hillsman, Deane; Biological Psychology, v.43, Issue 3, Jun. 28, 1996, p.243-244).
Prior art with simple Tidal Volume visual biofeedback means has demonstrated effectiveness in weaning patients from ventilator dependancy (See: "The Reduction of Weaning Time from Mechanical Ventilation Using Tidal Volume and Relaxation Biofeedback;" Holliday, Jerome E. and Hyers, Thomas M.; American Review of Respiratory Diseases, 1990; v.141: p.1214-1220). The instant invention enhances this concept by sophisticated breathing pattern training.
Prior art traditional weaning techniques indicates the probability that some patients in the so-called "difficult to wean" category suffer from one or another form of poorly understood respiratory center dysfunction produced by severe illness such as shock, sepsis, etc. It is also apparent that the mode of ventilation used on these patients can have a significant influence, and in some manner may produce an undesirable breathing pattern imprint within the respiratory center which carries over into the weaning period.
In addition, many patients who fail to wean are known to have excessive neurologic drive from the respiratory center as measured by increased inspiratory effort by the so called P 0.1 test (the inspiratoxy pressure generated after a 0.1 second breath interruption) and increased electromyogram (EMG) activity of respiratory muscles. It seems this is probably in part related to corrupted neurologic driving signals from the respiratory center sending out strong but poorly coordinated and/or otherwise improper breathing pattern signals. An expression of this dysfunction is inefficient immediate rapid and shallow breathing displayed by many patients who fail to wean after being removed from ventilatory support, even though their respiratory muscular strength and pulmonary mechanics can be demonstrated to be adequate, and also by some erratic breathing patterns during this process. The instant invention provides proper breathing patterns to these patients as a model they will be able to follow, and therefore maintain adequate ventilation and permit effective participation the weaning process. And during this time the respiratory center will also be undergoing a training or reconditioning process to become more functional, thus further expediting complete removal from ventilatory support.
Ventilator dependence is a serious medical and economic problem. It is well known that severe and sometimes lethal complications may develop the longer a patient is on ventilator support. In addition, as ventilator therapy is provided in specialized and very expensive Intensive Care Unit environments, there is a strong economic need to minimize ventilator dependency. The instant invention therefore improves patient safety and minimizes expenses by more efficiently weaning patients from ventilator dependence.
While the instant invention is designed to work mainly with patients undergoing spontaneous breathing trials, it may also be used in patients undergoing weaning trials with partial assist from various ventilator devices. For example the so-called Proportional Assist Ventilator, or a ventilator with optional so-called Intermittent Mandatory Ventilation (IMV) or so-called Pressure Support Ventilation or similar modes, or an external non-invasive (i.e. no endotracheal tube or tracheostomy) ventilator such as the commercial BiPap device or a standard pressure controlled Intermittent Positive Pressure Breathing (IPPB) device used with a face mask, or a cuirass type ventilator. All of these prior art ventilators sense and/or adjust for respiratory deficiency in various ways, and provide appropriate inspiration assist breaths. But none of these ventilators provide direct patient incentives to breathe in a natural manner, and therefore are less efficient in the weaning process. The instant invention provides appropriate breathing prompting signals, and, when the patient fails in the weaning process the various independent safety and supportive functions of these ventilators become operative. In addition the instant invention could be used to more efficiently trigger the ventilatory supportive features of a plurality of prior art ventilators.
Prior art ventilator weaning monitoring methods are dearly inadequate, depending on subjective impressions of clinical fatigue or distress and/or arterial blood gas derangements that of necessity measure failure after the failure has already developed. More modem monitoring techniques such as the ratio of Tidal Volume to Respiratory Rate are still relatively crude indices of weaning performance. Weaning from ventilator dependency is potentially hazardous due to unexpected precipitous ventilatory failure, and early warning by appropriate monitoring means is imperative for patient safety. Further, controlled stress of weakened respiratory muscles is imperative in order to recondition these muscles, but in addition to not over-stress these fragile recovering muscles and therefore cause further damage. It is often difficult to safely define the proper degree of weaning stress clinically. The instant invention permits ideal levels of ventilation to be defined, as well as minimum safe levels of ventilation, and to provide visual monitoring and appropriate alarm signals of hazardous suboptimal ventilation on a breath by breath basis, prior to catastrophic and hazardous overall ventilatory failure. Patient performance is monitored using the so-called "Phantom Line" concept of performance quality control by use of visual plus and minus volumetric error limits. If instructions and encouragement from the caregivers fails to promptly correct the patient to a minimum safe level of ventilation, a physiologically appropriate level of fatigue is defined, and the weaning trial may be terminated prior to the development of excessive respiratory muscle fatigue. This will avoid the problem of excessive exhaustion with catastrophic and dangerous respiratory failure.
In the alternative, it may sometimes be desirable to extend the weaning period to maximally stress the patient's respiratory muscles. Prior art stressing techniques are highly subjective and not well defined, and are therefore in danger of producing excessive and damaging stress to the recovering respiratory muscles. The instant invention can define a maximum stressing goal by instantly substituting a visually similar breathing pattern with a smaller Tidal Volume breath and higher Respiratory Rate, which is the normal breathing pattern defense mechanism for fatiguing respiratory muscles. In this case a new level of optimal and minimal safe ventilatory level is defined and monitored to insure patient safety. When the patient demonstrates breath by breath ventilatory failure while using the natural defensive breathing pattern, a dear level of maximal stress has been defined and the weaning trial terminated.
Traditional prior art methods in acutely decompensated patients to avoid the need for invasive ventilatory support (i.e. with endotracheal intubation or tracheostomy) are clearly suboptimal. Typically a patient with emphysema and an acute bronchitic exacerbation is hospitalized with respiratory distress and a potential for need of life saving ventilatory support. However, it is well known if that patient can be managed for the first critical 24 hours by conservative means while various therapeutic modalities be given time to work, invasive ventilation can frequently be avoided, thereby avoiding well known ventilator complications and attendant increased cost. Typically these patients are struggling to breathe, and in so doing are resisting external ventilatory support means (e.g. the commercial BiPap device or a standard Intermittent Positive Pressure Breathing (IPPB) device) by poorly coordinated breathing that is out of phase with ventilator action, and therefore impairing the proper functionality of the vital external ventilation support. The same biofeedback system of the instant invention could be used equally as well in breathing control of these patients in acute respiratory failure, to coordinate patient and ventilator synchrony and thereby optimize ventilator action. Monitoring of such patients is likewise critically important and is similar to the monitoring as described with weaning protocols, but in this case the ventilatory failure parameters as described would result in a definable and logical decision for the need to intubate.